Field of the Disclosure
The present disclosure relates generally to synchronization of a received signal and more particularly to detection of a preamble of a received signal.
Background of the Disclosure
Communication of a signal or multiple signals over a medium can be performed by modulating a carrier frequency with a signal to be communicated. The modulating signal varies the actual instantaneous frequency being transmitted from the carrier frequency. For communication to occur efficiently, a receiver should be set to the same carrier frequency as the carrier frequency on which a transmitter is transmitting. Thus, a receiver can have a technique for fine-tuning its carrier frequency. However, if a carrier frequency is modulated with a signal that varies slowly, the variation of the carrier frequency can persist long enough that the actual instantaneous frequency can be mistaken as the carrier frequency being modulated by the receiver's technique for fine-tuning the receiver's carrier frequency. Such confusion can cause the modulating signal to appear as a tone or series of tones and can be referred to as tone interference.
One example of tone interference is external tone interference. External tone interference can occur, for example, when a slowly varying modulating signal, such as an FSK signal emitted by a key fob at a very low data rate, appear as a series of tones to a receiver, such as with a Bluetooth Low Energy (BLE) device.
Another example of tone interference is self-tone interference. Self-tone interference can occur, for example, when a long string of 1's or 0's occurring anywhere in a frame delimiter appears like a tone at ±fdev where fdev is the frequency deviation.
A data transmission can begin, for example, with a preamble having a predetermined, typically simple, pattern, such as alternating different symbols. A receiver can prepare to receive data when it detects the presence of such a preamble. The receiver can use a known reference waveform based on the pattern of the preamble to detect the presence of a preamble. The receiver can adjust its receive frequency using a carrier frequency offset (CFO) estimate to compensate for frequency error between a transmitter and the receiver. However, tone interference can produce high correlations with the reference waveform, e.g., higher than a preamble does, which can result in false preamble detection events and incorrect CFO estimation. Consequently, a subsequent frame delimiter may not be successfully detected. A high degradation in synchronization performance may be observed due to this problem.
Simple methods based on a comparison of correlation values may be inadequate to solve the problem.
The use of the same reference symbols in different drawings indicates similar or identical items.